1. Field of the Invention
The present invention relates to a wireless reception device that is used in wireless communications such as mobile communications, cellular phones, satellite communications, microwave relay devices and which automatically establishes frequency synchronization or phase synchronization and, more particularly, to a wireless reception device which detects a synchronous and asynchronous state of an automatic frequency control circuit for controlling the frequency synchronization or the synchronous and asynchronous state of a carrier recovery circuit that controls phase synchronization and which establishes a synchronous state automatically in the event of an asynchronous state.
2. Description of the Related Art
It is known that, in a wireless communication device, a deviation exists between the frequency on the transmission device side and the frequency on the reception device side and that there is degradation of the bit error rate (BER) due to the effect of this frequency deviation. Therefore, a demodulation device on the reception side removes the frequency deviation between transmission and reception by means of an automatic frequency control (AFC: Automatic Frequency Controller) circuit. Further, a phase error or phase shift similarly exists between the transmission and reception sides and the demodulation device removes this phase error by means of a carrier recovery circuit or the like.
This method of removing the frequency deviation appears in Japanese Patent Application Laid Open Nos. H6-244820 and 2002-237767, for example. These patent documents describe a method that resolves the difficulty of frequency synchronization pertaining to a case where a code division multiple access (CDMA) system is used.
An AFC circuit constitutes an AFC loop comprising a phase rotation device, a frequency discriminator, and a voltage control oscillator, wherein the frequency discriminator finds the frequency deviation component from a received modulation signal that has been frequency-converted to the baseband, the voltage control oscillator (VCO) generates an AFC reference signal with a frequency corresponding to the frequency deviation component, and the phase rotation device removes the frequency deviation component by performing phase rotation corresponding with the frequency deviation from the reception modulation signal by using an AFC reference signal.
A variety of noise and interference signals, and so forth, exist in the wireless transmission channel and the frequency synchronization of the AFC circuit is sometimes off as a result of the effect of the noise and interference signals. More particularly, in the case of mobile communications and cellular phones and so forth, blocking of sudden signals caused by a cover structure is produced and the synchronization of the AFC circuit is readily off. Further, because very weak electric waves are used in satellite mobile communications and so forth, there are frequent cases where recovery to a synchronous state is difficult once the synchronization of the AFC circuit is off.
Generally, in a fixed period from the time an arriving electrical power is detected, the AFC loop performs a locking operation for the frequency caused by the recovery control operation and removes the frequency deviation so as to establish frequency synchronization. During the locking operation, the frequency band is widened so that the locking of the frequency is rendered simple and, once locking is complete, the frequency band is narrowed to establish a steady state and the stabilized locking state (synchronous state) is maintained. The switch from the initial locking state to the steady state after synchronization has been established is performed with timing that counts a fixed time determined beforehand after detecting the arrival of reception waves.